Project 4 In order to investigate the mechanisms by which inflammation, oxidative stress, and nitric oxide in particular contribute to cancer risk, we have developed a series of mouse models of colitis and colitis-associated cancer. We will use highly susceptible compound mutant mice deficient for interleukin 10 (IL10) and recombination activating gene 2 (Rag2) on a 129/SvEv background. These 129/SvEv ILIO'^Rag"'" mice develop lesions that resemble inflammatory bowel disease (IBD) and cancer when infected with Helicobacter hepaticus or after adoptive transfer with CD4*CD45RBhigh effector T cells (Teff). We will also use IL10"'" mice on a C57BL/6 background infected with Helicobacter trogontum and wild type C57BL/6 mice infected with Citrobacter rodentium. For all three mouse models, the gpt delta reporter transgene will be used to quantify and characterize somatic mutations that arise in vivo. A novel Fluorescent Yellow Direct Repeat (FYDR) transgene will also be generated in order to quantify recombination events in vivo. We will characterize the role of inducible nitric oxide synthase (iNOS) in 129/SvEv ILIO^'Rag"'" mice infected with H. hepaticus that develops a rapid onset of colitis-associated cancer, C57BL/6 IL10"'" mice infected with H. trogontum that develops IBD, and C57BL/6 mice infected with C. rodentium that develops a self-limiting colitis. This will be accomplished by pharmacologic inhibition of NOS enzymes as well as by crossing our C57BL/6 models with iNOS"'" mice. Depletion experiments will also be carried out to ascertain the role of neutrophils and macrophages in colitis and cancer in these model systems. These experiments will provide specimens for the other Projects in this Program in order to validate computational models, characterize chemical biomarkers, and establish the role of DNA damage and repair in mutagenesis. By establishing the role of nitric oxide produced by inflammatory cells and by epithelial cells in the large intestine, we will gain a better understanding of the mechanistic basis of cancer risk in IBD, and in mucosal inflammation in general. These studies and the interactions with the other Projects in the Program should translate into newstrategies to prevent the initiation or delay the progression of inflammation-associated cancer.